Floods are defined by maximum water levels or flow of high-water waves. Here, we defined the deterministic method for the calculation of the probability of a high discharge event, named as the Probability Of Success (POS). The POS method previously developed for petroleum subsurface systems has been modified for the surface hydrological system with the purpose of flood prediction. The case study of this research is the small basin of Kašina Stream on Medvednica Mt. (NW Croatia). The data are obtained upstream from the hydrological station Gornja Kašina. The POS model is defined by four categories. Each geological category is described with accompanied events and probabilities. Floods are defined by four categories: total precipitation, total water flow, basement, and maximal water capacity in soil. The categories total precipitation and basement were divided into two sub-categories each: quantity and duration; porosity and soil depth. Data are collected for a hydrometeorological event, namely an intensive convective storm on 24–25 July 2020, when Zagreb was locally hit by heavy urban floods. The presented probability method yielded a probability of 1.76% that such an event could happen to the station. However, the flooding was not recorded. A comparison of the real event and the predicted probability supported the adequacy and applicability of the method, showing it has high reliability. The presented probability model could be easily applied, with small modifications, to the entire area of Northern Croatia for the prediction of small basin flooding events.

Biokovo Mountain in Croatia is a Dinaric hotspot of subterranean biodiversity and its area of 196 km 2 is protected as a nature park. Until now, more than 400 caves have been registered here, however, only in about 30% of them biospeleological research has been carried out. It is hypothesized that over 1000 caves exist in highly karstified Biokovo Mt. Biospeleological research of the area started at the beginning of 20th century and deep caves were infrequently explored after the year 1980. Previous research recorded more than 90 troglobiotic species in this area and most of them are endemic. The primary goal of the Expedition was a systematic survey of eight deep caves (depth over 250 m), one of which was never before biospeleologically surveyed. We also surveyed other caves from which material for detailed faunistic analysis was missing. The main part of the expedition took place from 17 th to 25 th June 2017, with 52 participants. Fauna was collected by hand and by pitfall traps with baits, in the total of 26 caves. Five deep caves were completely surveyed (depth up to 710 m), the topographic map was made when missing, and fauna was photographed. Microclimatic conditions were measured and in two caves data loggers were placed. According to preliminary results, around 10 new species for science have been found from following groups: leeches (Hirudinea), spiders (Araneae), harvestmen (Opiliones), woodlice (Isopoda), centipedes (Chilopoda), springtails (Collembola), two-pronged bristletails (Diplura) and beetles (Coleoptera). These results confirm that deep caves of Biokovo Mt are still underexplored and that detailed and systematic research is needed.